Topological structural transformation of a two-dimensional coordination polymer via single-crystal to single-crystal photoreaction.

Photoreactive coordination polymers are particularly important media for the implementation of highly-selective photoreactions and creation of photoresponsive intelligent materials and devices. Herein, a two-dimensional (2D) photoreactive coordination polymer, formulated as [Cd(pha)(3,3'-bpe)] n (1) was prepared through the hydrothermal reaction between Cd(NO 3 ) 2 ·4H 2 O, phthalic acid (H 2 pha) and 1,2-bis(3-pyridyl)ethylene (3,3'-bpe). Upon exposure to 365 nm UV light, the 1 H NMR spectroscopy and single crystal X-ray diffraction analysis results indicated that 1 can undergo a [2 + 2] photocycloaddition reaction and thus form a new coordination polymer [Cd(pha)(3,3'-tpcb) 0.5 ] n (1a) through single-crystal to single-crystal (SCSC) transformation. Accompanied by the SCSC photoreaction, the 2D sql net of 1 converted into a 2D binodal network of 1a with the rare (3 2 4·6 2 7)(3 2 6 2 7 2 ) topology. The SCSC transformation from 1 to 1a also exhibits an interesting photocontrolled fluorescence. The unique photoinduced structural change and fluorescence quenching of 1 makes it a potential intelligent material for optical anti-counterfeiting, fluorescence sensors and other fields.